1. Field of the Invention
The present invention relates to solar power production, and more particularly, to solar receiver panels for use in solar boilers.
2. Description of Related Art
Solar power generation has been considered a viable source to help provide for energy needs in a time of increasing consciousness of the environmental aspects of power production. Solar energy production relies mainly on the ability to collect and convert energy freely available from the sun and can be produced with very little impact on the environment. Solar power can be utilized without creating radioactive waste as in nuclear power production, and without producing pollutant emissions including greenhouse gases as in fossil fuel power production. Solar power production is independent of fluctuating fuel costs and does not consume non-renewable resources.
Solar power generators generally employ fields of controlled mirrors, called heliostats, to gather and concentrate sunlight on a receiver to provide a heat source for power production. A solar receiver typically takes the form of a panel of tubes conveying a working fluid therethrough. Previous solar generators have used working fluids such as molten salt because it has the ability to store energy, allowing power generation when there is no solar radiation. The heated working fluids are typically conveyed to a heat exchanger where they release heat into a second working fluid such as air, water, or steam. Power is generated by driving heated air or steam through a turbine that drives an electrical generator.
More recently, it has been determined that solar power production can be increased and simplified by using water/steam as the only working fluid in a receiver that is a boiler. This can eliminate the need for an inefficient heat exchanger between two different working fluids. This development has lead to new challenges in handling the intense solar heat without damage to the system. One such challenge involves the fact that traditional boilers are made up of multiple individual boiler panels sized to facilitate manufacture and maintenance. The intense heat fluxes in solar applications can be around 2-3 times higher than in typical fossil fuel boilers. Additionally, unlike fossil fuel boilers, solar boilers operate on a daily cycle, shutting down in the night. The high heat fluxes and frequency of operation cycles create challenges with respect to managing thermal expansion and contraction of the boiler panels. One such challenge is that panels expand vertically along their length as well as laterally across their width. If gaps are used between panels to allow for their thermal expansion, care must be exercised to protect structures and spaces behind the panels from solar radiation passing through the gaps, which is known as leakage. Also, gaps in the receiver area of a boiler constitute area where available sunlight from the heliostats is not captured.
While previously known systems of solar power production have generally been considered satisfactory for their intended purposes, there has remained a need in the art for solar receivers that can improve the accommodation of thermal expansion and protect the boiler from leakage of solar radiation. There also has remained a need in the art for such solar receivers that are easy to make and use. The present invention provides a solution to these problems.